Contest Situations Research Articles

Short-term responses of plasma norepinephrine, epinephrine, glucocorticoid and testosterone titers to social and non-social stressors in male guinea pigs of different social status

The short-term effects on norepinephrine (NE), epinephrine (E), glucocorticoid (CS) and testosterone (T) levels of (a) taking blood samples, and (b) an agonistic encounter in an experienced fighter's home cage were examined in 15 male guinea pigs living in large heterosexual colonies for 8 to 19 months. Four tests were performed 1 month apart. In the 1st, 2nd and 3rd test 3 blood samples were taken from each male in a strange room within 30 min (sampling times were designated as 0, 20 and 30 min, respectively). In the 4th test blood samples were taken on the same time schedule, however, the males were given 10 min agonistic encounters 10 min after the initial blood sampling. The main findings were as follows: (1) in response to taking blood samples and fighting CS and NE titers increased significantly, whereas E values did not change in a significant way. T titers decreased 10 min after the agonistic encounter. (2) The % changes of NE, E, CS and T at 20 and 30 min did not differ whether an agonistic encounter took place or only blood samples were taken. (3) According to their behaviors displayed in the colonies the males were divided into high (N=6) and low (N=9) ranking individuals. When only blood samples were taken the males' social status was only reflected by a tendency towards higher T levels in high ranking males, however not by NE, E and CS titers. (4) High ranking males showed lower NE titers than low ranking males directly after the agonistic encounter. No further relationships between long-term social status and short-term endocrine responses were found. (5) According to their behaviors displayed during the agonistic encounters the males were divided into fighters (F) (5 out of 6 high and 3 out of 9 low ranking individuals), and non-fighters (NF) (1 high, 6 low ranking individuals). F and NF did not differ in T and CS values, NE titers, however, were significantly higher in NF compared with F before, directly after the encounter as well as 10 min later. E was significantly higher in NF than in F directly after the encounter. One month before the contest prospective NF showed higher NE levels at 0, 20 and 30 min sampling times than prospective F when only blood samples were taken. These findings point to a more important role of catecholamines than CS and T in guinea pig intermale agonistic encounters. NE responsiveness may have predictive value for the behavior in contest situations.

ON THE DEFINITIONS AND FUNCTIONS OF DOMINANCE AND TERRITORIALITY

Summary1. Dominance/subordinance is a relationship between two individuals in which one defers to the other in contest situations. Each such relationship represents an adaptive compromise for each individual in which the benefits and costs of giving in or not giving in are compared. Familiar associates in groups or neighbours on nearby territories may develop relatively stable dominant‐subordinate relationships based on individual recognition. Although the aggressive aspects of dominance are usually emphasized, the less conspicuous actions of the subordinate individual are actually more important in maintaining a stable relationship.2. In evolutionary terms, dominance essentially equals priority of access to resources in short supply. Usually the subordinate, who would probably lose in combat anyway, is better off to bide its time until better able to compete at another time or another place. Both individuals save time, energy, and the risk of injury by recognizing and abiding by an established dominant‐subordinate relationship.3. Dominance can be either absolute or predictably reversible in different locations or at different times. Of the various forms of dominance behaviour, rank hierarchies and territoriality represent the two extremes of absolute and relative dominance, respectively. A dominance hierarchy is the sum total of the adaptive compromises made between individuals in an aggregation or organized group. Many animals seem to be capable of both absolute and relative dominance, and within species‐specific limits the balance may shift toward one or the other. High density, or a decrease in available resources, favours a shift from relative to absolute dominance. Some species may exhibit both simultaneously. Social mammals may have intra‐group hierarchies and reciprocal territoriality between groups, while the males of lek species may exhibit ‘polarized territoriality’ by defending small individual territories, with the most dominant males holding the central territories where most of the mating takes place.4. Territoriality is a form of space‐related dominance. Most biologists agree that its most important function is to provide the territory holder with an assured supply of critical resources. Territoriality is selected for only when the individual's genetic fitness is increased because its increased access to resources outweighs the time, energy, and injury costs of territorial behaviour.5. Territoriality was first defined narrowly as an area from which conspecifics are excluded by overt defence or advertisement. The definition has been variously expanded to include all more or less exclusive areas without regard to possible defence, and finally to include all areas in which the owner is dominant. I define territory as a fixed portion of an individual's or group's range in which it has priority of access to one or more critical resources over others who have priority elsewhere or at another time. This priority of access must be achieved through social interaction.6. My definition excludes dominance over individual space and moving resources, and includes areas of exclusive use maintained by mutual avoidance. It differs from most other definitions in its explicit recognition of time as a territorial parameter and its rejection of exclusivity and overt defence as necessary components of territorial behaviour. There is an indivisible continuum of degrees of trespass onto territories, and functionally it is priority of access to resources that is important rather than exclusive occupancy.7. There is a similarly indivisible continuum in the intensity of behaviour needed to achieve priority of access to resources. Deciding whether or not an exclusive area is defended leads to the pointless exercise of trying to decide which cues indicating the owner's presence are conspicuous enough to merit being called defence. Concentrating on overt defence emphasizes the aggressive aspects of territorial behaviour rather than the equally or more important submissive aspects such as passive avoidance.

The role of asymmetries in animal contests

This paper contains a game theoretical analysis of animal contest situations which are asymmetric in more than one aspect: two opponents may for example be imagined which differ in ‘ownership status’ as well as in ‘relative fighting ability’. The following question is analysed: which aspect may or must be used for conventional settlement in a population ‘playing’ an evolutionarily stable strategy (ESS)? The contestants are assumed to be fully informed about the asymmetric features. In particular, the assessment of relative fighting ability is supposed to be unambiguous and without cost. This assumption of perfect information allows for a decomposition of the ‘evolutionary game’ into sub-games. Therefore an easy procedure for calculating the ESS's can be presented, and simple models are analysed. It is concluded that payoff-irrelevant aspects may be used for conventional settlement of a conflict even if payoff-relevant asymmetric aspects also exist. One of the aspects may, however, be of such strong relevance that, no matter which ESS is played, animals must base their decisions on that ‘dominant’ aspect. It may also occur that two different asymmetric features are each of strong payoff relevance for either of the opponents, such that they have no escalation-suppressing effect. The particular scenario of a conflict between an ‘owner of a resource’ and an ‘intruder’ is used to derive the more general conclusions.

The logic of asymmetric contests

A theoretical analysis is made of the evolution of behavioural strategies in contest situations. It is assumed that behaviour will evolve so as to maximize individual fitness. If so, a population will evolve an ‘evolutionarily stable strategy’, or ESS, which can be defined as a strategy such that, if all members of a population adopt it, no ‘mutant’ strategy can do better. A number of simple models of contest situations are analysed from this point of view. It is concluded that in ‘symmetric’ contests the ESS is likely to be a ‘mixed’ strategy; that is, either the population will be genetically polymorphic or individuals will be behaviourally variable. Most real contests are probably asymmetric, either in pay-off to the contestants, or in size or weapons, or in some ‘uncorrelated’ fashion; i.e. in a fashion which does not substantially bias either the pay-offs or the likely outcome of an escalated contest. An example of an uncorrelated asymmetry is that between the ‘discoverer’ of a resource and a ‘late-comer’. It is shown that the ESS in asymmetric contests will usually be to permit the asymmetric cue to settle the contest without escalation. Escalated contests will, however, occur if information to the contestants about the asymmetry is imperfect.

Education at Harvard

cratic society in which most of the winners would have high morale because in a contest situation they gained their places by socially defined merit. But he also saw a revolt by some disenchanted winners, who included a few surly, old-fashioned Populists and romantic high-status women, who would side with the losers and lead the revolt. Meritocracy is both a procedure for distributing scarce educational and occupational resources and for determining how the work of society shall get accomplished in an intricate, still largely industrial world. It has acquired a pejorative connotation, although it is often unclear what the critic would put in its place as a mode of distributing scarce positions and opportunities in a nation of 220-million people linked to a world economy. Sometimes there is the implication that all people are in some sense equal in merit, as I believe people to be in a basically religious sense. Sometimes merit is defined too narrowly, even if one focuses on the allocation of scarce resources. But other criti-